The invention relates generally to the art of earth boring through subterranean areas, such as beneath sidewalks, roadways, etc. More particularly, the invention is concerned with a coupling to be utilized in coaxially joining pipe or rod sections which coupled sections are then driven by an earth boring drive unit to carry out the boring operation.
The type boring operations contemplated herein are particularly useful in laying pipelines or other conduits beneath paved highway or sidewalk surfaces in that they avoid the necessity of digging up the ground surface to form a trench for the conduit with resulting need for back filling the earth and possibly then repaving the surface over the trench location. To exemplify the type boring operation in which the coupling invention herein may advantageously be used, note may be made of Martin et al U.S. Pat. No. 4,000,879 which discloses a pushing or pulling apparatus and Kandle U.S. Pat. No. 2,639,931 which discloses a rotary drilling approach to earth boring. Both use a sectionalized pipe or rod with the sections being coaxially coupled to successively increase the length of pipe or rod required for earth boring. But, as will be apparent from the following disclosure, the coupling of this invention is useful primarily in rotary boring operations where the pipe or rod must be pushed and pulled, but the primary power transmission is in rotating the pipe or rod.
In the above types of boring operations, it will be readily appreciated that the coupling employed between the adjoining ends of the pipe or rod sections that must be coaxially connected is subjected to severe stresses in driving the coupled sections through the earth. The typical boring operation requires the coupling and uncoupling of several sections of drill pipe or rod which can be a time consuming and difficult operation. Still, the coupling joint has to be capable of withstanding the severe stresses that are encountered in boring to provide a reliable joint which will hold the pipe or rod sections together while the boring is taking place. Typically in these boring operations the first section of drill pipe or rod is connected to the earth boring drive unit which is either in the form of a rotating input unit or unit which pushes the pipe or rod along its axis to carry out the subterranean boring.
Recognizing the above mentioned stresses to be encountered by the coupling coaxially joining the pipe or rod sections, it is necessary that the coupling be capable of withstanding high axial compressive loads where the drive unit pushes the pipe along its axis and be capable of transmitting high torque loads where a rotary earth boring drive unit is employed to carry out subterranean boring. In both cases, it is important that the coupling be free from jamming even under the high load stresses encountered. Too frequently the couplings proposed in the prior art have either failed or have been prone to jamming under stress loads thereby rendering it difficult if not impossible to freely separate the coupled pipe or rod sections as necessary following the boring operation.
It is also important that the coupling used in joining the pipe or rod sections be capable of being quickly joined by hand and easily released, preferably without the necessity for utilizing special tools. These desired advantages for earth boring couplings have also been found locking in the prior art proposals.